1. Field of the Invention
The present invention relates to a hydrogen sensor, and particularly to a hydrogen sensor for detecting a very small amount of hydrogen. The present invention also relates to a method for measuring hydrogen concentration using the sensor.
2. Description of the Related Art
Sensors that include hydrogen-absorbing materials are already known. Physical properties, such as electrical resistance, weight, and strain (internal stress), of the hydrogen-absorbing materials vary during the hydrogen absorption and thereby the sensors can detect the amount of hydrogen.
Japanese Unexamined Patent Application Publication No. 2003-156461 discloses a sensor having a thermoelectric element for detecting an exothermic value. The thermoelectric element detects a temperature increase caused by hydrogen absorption as a thermoelectromotive force.
However, temperature variations of a hydrogen-absorbing material may change the hydrogen absorbing characteristics, in particular, an initial hydrogen partial pressure of the hydrogen absorption; therefore, the hydrogen concentration derived from the variations in the physical properties of the hydrogen-absorbing material may undesirably vary over time.
In conventional techniques, the variations in the hydrogen absorbing characteristics must occasionally be compensated for as a result of the temperature variation. This makes the precise measurement of the hydrogen concentration difficult.
This problem can be overcome by keeping the temperature of the hydrogen-absorbing material constant. When the electrical resistance of the hydrogen-absorbing material is utilized, for example, the measurement requires “an electrical resistance detector,” “a cooler,” “a temperature controller,” and “a unit for calculating hydrogen concentration.” That is, a cooling system and a temperature controller must be introduced, making an apparatus and a circuit more complex.